Bisexual behavior in male rats treated neonatally with antibodies to luteinizing hormone-releasing hormone

For investigating the possibility that the neuropeptide luteinizing hormone-releasing hormone (LHRH) is involved in the process of sexual differentiation, male rat pups were injected on Days 1 and 3 of life with specific antibodies to LHRH (AB-LHRH); control rats were treated with normal rabbit serum (NRS). At maturity, males treated with AB-LHRH were as fertile as controls, and their amount and intromission latencies and the postejaculatory interval were extended only slightly. However, they showed high levels of lordotic behavior, including ear wiggling, when castrated and primed with estrogen or with estrogen plus progesterone. Testosterone propionate, administered neonatally together with AB-LHRH, did not reverse these effects. There was no evidence that neonatal treatment with antiserum to LHRH affected testosterone levels, as measured by radioimmunoassay. Males treated with AB-LHRH and castrated as adults did not respond to estrogen priming by releasing a surge of luteinizing hormone, a result indicating that they did not possess the female type of gonadotropin regulation. These findings indicate that neutralization of endogenous LHRH during neonatal life selectively blocks defeminization of behavior without affecting the process of masculinization.